Jeff Masters: 2012 was the warmest and 2nd most extreme in U.S. history

by Jeff Masters, Ph.D., WunderBlog, January 8, 2013

The contiguous U.S. smashed its record for hottest year on record in 2012, according to NOAA's National Climatic Data Center (NCDC). The annual U.S. average temperature was 3.3 °F above the 20th century average, and was an astonishing 1.0 °F above the previous record set in 1998. It is extremely rare for an area the size of the U.S. to break an annual average temperature record by such a large margin. Nineteen states, stretching from Utah to Massachusetts, had annual temperatures which were record warm. An additional 26 states had a top-ten warmest year. Only Georgia (11th warmest year), Oregon (12th warmest), and Washington (30th warmest) had annual temperatures that were not among the ten warmest in their respective period of records. As wunderground's weather historian Christopher C. Burt reported, of the approximately 5,500 U.S. stations in the NCDC database, 362 recorded their all-time highest temperature during 2012, and none recorded an all-time coldest temperature. This was the most since the infamous Dust Bowl summer of 1936. Approximately 7% of the contiguous U.S. experienced an all-time hottest day during 2012, and every state in the contiguous U.S. except Washington had at least one location experience its warmest year on record. One notable warmest year record occurred in Central Park, in New York City, which has a period of record dating back 136 years.

The 2012 weather was also very dry, and the year ranked as the 15th driest year on record for the contiguous U.S.  Wyoming and Nebraska had their driest year on record, and eight other states had top-ten driest years. The area of the contiguous U.S. experiencing moderate-to-exceptional drought peaked at 61.8% during July. This was the largest monthly drought footprint since the Dust Bowl year of 1939. 


Figure 1. Historical temperature ranking for U.S. states in 2012. Nineteen states had their warmest year on record, and an additional 26 were top-ten warm. Image credit: National Climatic Data Center (NCDC).


Figure 2. Temperatures for the contiguous U.S. in 2012, compared to the previous record warmest and coldest years in U.S. history. The annual U.S. average temperature was 3.3 °F above the 20th century average, and was an astonishing 1.0 °F above the previous record, set in 1998. It is extremely rare for an area the size of the U.S. to break an annual average temperature record by such a large margin. Image credit: NOAA/NCDC.

Second most extreme year on record
The year 2012 was the second most extreme on record in the contiguous U.S., according to NOAA's U.S. Climate Extremes Index (CEI), which tracks the percentage area of the contiguous U.S. experiencing top 10% and bottom 10% extremes in temperature, precipitation, and drought, plus winds from landfalling tropical storms and hurricanes. The CEI was 39% in 2012, approximately double the average of 20%. The only year that was more extreme since CEI record keeping began in 1910 was 1998 -- the United States' previous warmest year on record. Since Hurricane Sandy was not considered a hurricane when it came ashore, that storm did not contribute to the 2012 CEI. If one plots up the CEI without using the tropical storm and hurricane indicator, 2012 is the most extreme year on record, beating out 1998, 46% to 42%. During 2012, a record 87% of the contiguous U.S. had maximum temperatures that were in the warmest 10% historically, crushing the previous record of 62% set in 1934; 74% of the U.S. had warm minimum temperatures in the top 10% in 2012 (2nd highest on record.) The percentage area of the U.S. experiencing top 10% drought conditions was 34%, which was the 4th greatest since 1910. Only droughts in the Dust Bowl year of 1934, and during 1954 and 1956, were more extreme, averaged over the entire year. Heavy one-day downpours were near average in 2012, though, with 9% of nation experiencing a top 10% extreme, compared to the average of 10%.


Figure 3. NOAA's U.S. Climate Extremes Index (CEI) pegged 2012 as the second most extreme year on record, with 39% of the contiguous U.S. experiencing top 10% extreme weather. This is approximately double the average of 20% (heavy black line.)

http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=2324